January 05, 2010

Northwest Heat Wave and Cold Waves Back East

I am thinking of getting a palm tree for my house too!

I don't think it has escaped anyone's notice that is has been quite warm during the past four days...substantially above normal. Take a look at the temperatures since 25 December in the plot below for Seattle-Tacoma Airport. The time is in GMT (8hr later than PST) and the average daily highs and lows are shown by the red and blue lines. Since the new year began, our temps have been way above normal...with maximums getting near fifty and lows around 45. The average temps for this period are a high of 45 and a low of 36F. Our lows the last few days have generally been greater than the normal HIGHS. I am sweating just thinking about it. March temps in January.

Now at the same time the central and eastern U.S. is shivering under bitter cold temps--the media is full of cold wave and snowstorm coverage. Take a look at the max temps today across the U.S. in the graphic below. The west was balmy...50s in the NW to 70s in southern CA. The east coast was a different story..highest in the 20s and 30s in the NE and only in the very low 60s in southern FL. In the upper Midwest temps only rose into the single digits and teens.

This kind of pattern in which the west and east coasts are out of phase are not unusual at all. But why? The answer lies in the large scale circulation of the atmosphere ... something that is best seen aloft. The figure below shows conditions aloft at around half the pressure of the surface...this is a 500 millibar map (millibar is a unit of pressure) and it represents the height of this pressure above sea level. This pressure level is roughly at around 18,000 ft. The lines give you the height of this pressure surface above sea level. Where the heights are high there is a ridge, and where low, a trough. Winds tend to follow these lines with high heights to the right.
You will notice there is a ridge along the west coast and a broad trough over the eastern half of the country. Think of a rope held between two people...if one shakes it back and forth there is a wave-like pattern, with a ridge next to a trough. Generally, the nature of the flow is such that if we have a ridge they have a trough and vice versa..not always, but much of the time. On the western side of the trough the winds are blowing from the southwest and thus bring warm air northward, so the ridge tends to be warm. But on the back side of the ridge and western side of the trough the winds are from the north...bringing cold air southward, in this case into the eastern half of the U.S. We have been locked in this pattern for about a week...and with some minor changes it appears to be with us for a while.

And if you like warm here is more good news! The National Weather Service's Climate Prediction Center is going for a warmer than normal conditions for the remainder of the winter. Check out their graphic:
The major basis for this is the current El Nino..which brings warmer than normal temps to the northern tier of states..generally after Jan 1.

Perhaps we will have some early blossoms this year as a result of all this warmth...but I will leave that to the horticultural experts. I had a few plants savaged due to the cold wave in December, so hopefully we are finished with that!

Finally, the big weather of the meeting of the year is coming up...the Northwest Weather Workshop on March 5-6 in Seattle. This is where meteorologists and weather enthusiasts get together to talk about the weather of our region. So any of you could come. Information about the meeting, registration, fees, food, etc is found at:


Any of you in the vineyard business or agricultural pursuits and might be interested in giving a talk on how weather affects you....let me know. We are thinking of a having a session on such matters.


  1. Its obvious, El Nino. Slushy skiing.

  2. This is like 1992, when I came to Seattle expecting fresh powder snow. The whole winter was slush! That was an El-Nino year. Also, has anybody noticed what while this winter is really cold around the world, glaciers and icecaps have been melting for the past 30 years? I have pics to prove it from the N. Cascades. This El-Nino is different from other years. Melting glaciers and cold. A paradox.


  3. This could not be a bigger bummer. If I wanted to live in warmth during winter, I would have stayed in CA.

    I say: boo.

  4. I like this "break" in the winters personally.

    Nice hiking weather when the sun is out :)

    But...Q13 just said "windy" for Monday? Hmmmm........

  5. Very interesting Cliff. I know you have knowledge about the entire pacific NW (very cool book), but i wanted to share basic observations here just east of mountains in this el nino pattern.

    We have had extended periods of dry, but we have had four snowfalls of 6in. in between but melts. Not our typical sledding winter. Well over an inch of precip. the past 7 days. So we probably have above normal precip but its weird, because we have only had a few precip events, but when we do, it has really been wet "to our" standards.

    Temperature wise, its just been cool but not cold. Daytime highs have been below average but nightime lows way above average. I swear, we have been breathing the same air here since that cold snap and not felt a downslope west wind in months.

    The places that suffer the most are the mid slope regions that sit just above the valley inversions. I took a cool pic of yakima ridge (just above 4000ft.) east of town that sums up this entire winter. The peak was white, brown and bare midway, and white again near the valley.

  6. Athos, I say: where were you last year?

    Don't worry, we'll have more cold, snowy winters. Plus ça change, plus c'est la même chose...

    Personally, I'm enjoying the warmer weather and I'm grateful for it too. With my husband unemployed for almost a year now, and having been out of work five months in 2009 myself, we couldn't afford to heat the house through a hard winter this year. Colder outside would mean colder inside, and that's no fun with a toddler in the family.

  7. I'm a bit confused by your pressure plot. You say it is the height above sea level of the 500 mb pressure contour and that this height is roughly 18000 above sea level but the contours are all close to around 500. Is it actually the pressure in mbs at a constant elevation of 18000 ft? What are the units of the contours? Thanks!

  8. @JewelyaZ, I have been here for just under a decade. I don't think in all of that time we've gone a single winter without at least one dusting of snow. This year is shaping up to be the exception. I just like seasons. I've lived back East and in CA, and though I grew up in CA, I never liked that we didn't have real "seasons." The part that I find very odd about this place is that the more "wintery" weather has always seemed to happen in November or March, not actual "winter." I'm not sure why that is (maybe Cliff answers this in his book), but just looking through all of my photos, I can see that most of the dustings we have had (or snow days) did not happen in winter proper.

  9. @Fleetwood - The solid black contour lines, the height of the 500 mb pressure field, have units of dekameters (dam). Add a zero to the indicated height, e.g., 570 dam -> 5700 m, then multiply by 3.28 to get feet. So 5700 m x 3.28 ft/m = 18696 ft. So the 500 mb pressure field undulates through these differing height values as indicated by the map.


  10. Tree and pond frogs were singing yesterday at my place of work in Bothell

  11. It seems El Nino is playing out here as you and others have mentioned. But it also seems it is not sticking to its region wide effects in California or sw states as of yet. We are quick to say"we got this child figured out" when it plays to its part, but atmospheric doctors are scratching their heads in other clinics. Could it be that we can still be humbled by the weather?

  12. I've been waiting for you to address this, partly to see if you had any insight into last freeze dates. Would they, for example, come much sooner this year? If so those of us wanting to grow fruits and veggies in our gardens could get a head start. I realize a freak freeze could always occur, but am starting to think maybe planting before March 22 is the way to go.

  13. Prof. Mass, I found this on the Seattle Municipal Archives:


    It is a climate map from 1971 for the Seattle area.

  14. Athos-
    I agree with you, an entirely snowless winter around here is awful, and pretty rare. Even Portland has had snow this winter! Heck, Tacoma even recorded snow on Dec. 13th.

    The winter of 2002-03 (also an El Nino year) was pretty bad as well. There was a dusting of snow on March 7, 2003 east of Seattle, and that was it. Let's pray this winter isn't like that one...

  15. I'm in Mazama. It 1 degree and sunny and clear. Beautiful snow tho a little icy from a little melt on Tuesday.

  16. Here's a link to an interesting article providing a wider possible perspective exploring whether current anomalies are explained by the "Arctic Oscillation" - abnormal highs in the arctic & some northern areas, lows in other northern temperate areas, and lows in the antarctic:

    comment would be interesting.

  17. The thought of early blooms makes me nervous. When my fruit trees bloom early we almost always get a cold spell afterward that freezes them all off again. Result: no fruit in summer. :(

    Are there any stats on how often a later cold snap occurs when we have El Nino years?

  18. Plus...

    I remember a year when there was an ENORMOUS caterpillar population on trees everywhere after a winter where it wasn't really that "cold."

    Would this year be following that same pattern?

  19. Cliff,

    I know myself & other farmers who would be interested in having a conversation on weather & how it relates to our agricultural pursuits.

  20. That is a windmall palm, they are very hearty and do well in the Pacific NW as long as the soil is well drained.


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